CODEWITHSUNDEEP
javascriptmongodbdatemath
Lee Brindley
Lee Brindley

Reputation: 6502

Searching objects who's timestamp is greater than X days

I've burnt myself out this week pretty bad! I'm failing with fixing a bug which should be solved with some basic mathematics.

I have some "Event" objects in my mongodb database, they get created with a date field, in a pre-save hook I calculate the day of year number and place that onto the model. E.g.

Jan 1st = 1

Jan 5th = 5

Dec 31 = 365

Users of my app can search for events which are X days ahead of the current date. My query is something like:

{
     day_number: { $gte: start_day, $lte: end_day}
}

Now the end of the year has come up, there is a logic bug.

Let's say for the inputs Dec 22 to Jan 2

My query is going: 

{
    day_number: { $gte: 356, $lte: 2}
}

This of course returns no results, as no number is greater than or equal to 356 and less than or equal to 2.

Any suggestions on a fix for this that doesn't involve butchering a albeit broken but simple query?

Upvotes: 0

Views: 39

Answers (2)

haltersweb
haltersweb

Reputation: 3149

You could test if the end day is smaller than the start day and then adjust end day like so:

var start_day;
var end_day;
var numDaysInbetween = 0;
var day_number = {}

/* test 1 */
start_day = 50;
end_day = 55;

/* test 2 */
start_day = 356;
end_day = 2;

if (start_day > end_day) {
  end_day += 365;
}
day_number = { $gte: start_day, $lte: end_day };

alert(day_number.$lte - day_number.$gte);

Upvotes: 2

Jesper We
Jesper We

Reputation: 6087

A majority of the time calculations in computer systems use the number of milliseconds elapsed since the rather arbitrary date 1970-01-01 0:00 as a sortable time variable.

You could apply the same principle but use the number of days since 2016-01-01, which would make Jan 2 == day 367. This way the query needs no change, your "hook" just needs a small mod.

Upvotes: 1

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